For efficient performance of a wide variety of tasks, work vehicles such as agricultural tractors and industrial equipment have a large number of speeds. Usually, the operators of these vehicles prefer to have a large share of the forward speeds in the regular working zone of approximately five to fifteen kilometers per hour.
Often, these work vehicles use countershaft transmissions having numerous rotating components such as shafts, gears, clutches, and bearings. In the typical countershaft transmission, the power train includes a speed section connected to a range section. Commonly, the speed section precedes the range section and receives input power from the engine. The range section is used to select a range or series of operating speeds for the output power. For each selected setting of the range section, the speed section functions to select any one of the series of speeds.
There are many ways to improve the countershaft transmissions. By decreasing the change in energy level of the rotating components during a shift between different ranges, one can decrease the time required for the particular shift as well as increase the smoothness of the shift. Furthermore, by decreasing the number of components, one can decrease the amount of material required for assembling the transmission. Moreover, by increasing the compactness of the countershaft transmission, one can decrease the space required in the work vehicle for the transmission, thereby increasing the flexibility of fitting the transmission into the vehicle.
Currently, Funk Manufacturing Company produces and sells a countershaft transmission for agricultural tractors having eighteen forward speeds and nine reverse speeds. Seven of the forward speeds are included in the regular working zone. The transmission uses twenty-two gears and nine clutches arranged such that six clutches form the speed section and three clutches form the range section. Furthermore, one of the clutches is dedicated to providing a range containing exclusively the reverse speeds. Also, the shafts are staggered lengthwise with respect to each other such that they are supported for rotation by three walls that are assembled together to form the housing. The transmission is arranged so each gear ratio sequence is used exclusively either for decreasing, transmitting identical speed as, or increasing speed transmitted to the gear ratio sequence. A first range includes nine forward speeds. A second range includes nine forward speeds consecutive to the speeds of the first range. A third range includes nine reverse speeds. Therefore, a range shift between the forward speeds requires making the complete change in energy level between the different ranges.
U.S. Pat. No. 5,063,793 discloses a countershaft transmission having twenty-four forward speeds and twelve reverse speeds. Excluding an optional power takeoff, the preferred embodiment of the transmission uses twenty-five gears and ten clutches arranged such-that six clutches form the speed section and four clutches form the range section. The six clutches of the speed section are each arranged to provide six forward speeds and three reverse speeds, so no range is dedicated to providing exclusively reverse speeds. Also, the shafts are staggered lengthwise with respect to each other. The transmission is arranged so each gear ratio sequence is used exclusively either for decreasing, transmitting identical speed as, or increasing speed transmitted to the gear ratio sequence. Each of the four ranges includes consecutive groups of six forward speeds and three reverse speeds. Therefore, a range shift requires making the complete change in energy level between the different ranges.
Even with the improvements that have been made in the countershaft transmissions of work vehicles such as agricultural tractors and industrial equipment, it is still desirable to provide further decreases in the change in energy level of the rotating components during a shift between different ranges, decreases in the number of components in the transmission, and increases in the compactness of the transmission.